The present invention relates to an artificial valve for implantation in a patient's blood vessel, in particular an artificial heart valve, and specifically relates to an artificial valve system including such an artificial valve.
Artificial heart valves are generally designed to replace the natural heart valve and to perform its function over many years, preferably until the person (or animal) dies. Thus, besides the general requirement that artificial valves must be made from a material that is compatible with the patient's blood and tissue, the valve must furthermore be extremely reliable.
Typical artificial heart valves are strictly mechanical, such as mechanical mono- or bi-leaflet valves and ball valves. A leaflet valve may for instance comprise a tilting disc hinged to an annular ring that is sutured into the blood vessel. The blood pressure changes of typically between 80 mmHg and 120 mmHg cause the disc to swing between an open and a closed position. In ball valves, a ball is held in a cage and allowed to move therein upon blood pressure changes between a closed position in which it seals an annular ring sutured into the blood vessel and an open position in which the ball is at a distance from the ring, thereby permitting blood to flow around the ball.
While there are many different types of artificial valves for implantation in a patient's blood vessel, they all suffer from the draw back of material fatigue resulting in breakage of parts thereof. Disfunctioning of the valve is only one severe consequence thereof. The consequences may be fatal when broken parts are carried away with the blood stream and block the blood stream at remote locations. Another problem arising with artificial valves implanted in blood vessels is the danger of generating thromboses as well as fibrosis forming and growing on the valve elements. Particularly the latter may prevent complete closing of the valve, thereby causing valve insufficiency.
There has been suggested in WO 2007/051568 an artificial valve for implantation in a patient's blood vessel, in particular an artificial heart valve, which is mechanically reliable over a long period of time without its closing efficiency being substantially affected by fibrosis. It is further described therein an entire valve system comprising such an artificial valve and further components. The present invention is an improvement to the valve and valve system described in WO 2007/051568 and, therefore, the function of the known valve will now be described in detail insofar as it applies also to the present invention.
More specifically, the artificial valve known from WO 2007/051568 comprises a first and a second valve member, each having a first smooth surface. The first smooth surfaces of the first and second valve members face each other so as to form a sealing contact between the first and second valve members. The first and second valve members further each have at least one blood flow passage extending from the first smooth surface to a second surface located on an opposite side of the respective valve member, wherein the first valve member is arranged so as to be slidably displaceable relative to the fixedly mounted second valve member such that the passage of the first valve member can be brought into at least partial alignment with the passage of the second valve member while maintaining the sealing contact between the first and second valve members. The artificial valve further comprises a displacing mechanism for the relative displacement of the valve members so as to bring their blood flow passages into and out of said at least partial alignment.
This way, blood flow through the valve can be controlled by sliding displacement of the valve members relative to one another, thereby aligning and disaligning the blood flow passages, i.e. opening and closing the valve. The smooth surfaces forming the sealing contact and the fact that opening and closing of the valve is performed by sliding displacement of the smooth surfaces relative to each other prevent any fibrosis formation on the sealing surfaces. Thus, the sealing efficiency will not deteriorate over time. Furthermore, due to the valve members being displaced relative to one another in a sliding fashion, the forces acting on the valve members are relatively small, thereby overall reducing problems of fatigue of the valve member material.
In a preferred embodiment described in WO 2007/051568, the displaceable arrangement of the valve members relative to one another is such that the first valve member is rotatable relative to the fixedly mounted second valve member. This allows for the at least partial alignment and disalignment of their blood flow passages either by moving the first valve member back and forth in opposite directions of rotation or by continuously moving it in a single direction of rotation.
FIGS. 14 and 15 show the principle structure of such an artificial valve. The absolute and relative dimensions are not true to scale and the shape of the valve members may be chosen differently. The artificial valve 100 shown in FIGS. 14 and 15 comprises a first valve member 10 and a second valve member 20, composed of two halves 20a, 20b. The second valve member 20, here, forms a housing for the first valve member 10. The first valve member 10 is disc-shaped and arranged within the second valve member 20 for rotation about an axis 101, while the second valve member 20 is stationary. The first valve member 10 has a blood flow passage 13 extending from a first surface 11 to a second surface 12, and the second valve member has a blood flow passage 23a, 23b extending from a first inner surface 21 to a second outer surface 22. Upon rotation of the first valve member 10 about the axis 101, the blood flow passage 13 of the first valve member 10 may be brought into complete alignment with the blood flow passage 23a, 23b of the second valve member 20, thereby establishing flow communication through the valve 100 from an upstream side 105 to a downstream side 106 thereof. Centrally arranged within the artificial valve 100 is a displacing mechanism in the form of a motor M for displacement of the first valve member 10 relative to the second valve member 20 for turning the first valve member 10 either back and forth or always in the same direction. The displacing mechanism is contained in a cavity 102 which is formed and sealed against blood ingression by the valve members 10, 20. FIG. 15 shows the top view of the artificial valve 100 of FIG. 14, the blood flow passages 13, 23 each extending over 180° in an angular direction, more particularly somewhat less than 180° so as to prevent any flow communication between the blood flow passages 13, 23 when the valve 100 is in its closed position. The rotatably arranged first valve member 10 has to be turned by 180° to open and close the valve. Also, blood flow will be concentrated at one side of the valve 100.
It is preferred to divide the passages into a plurality of angularly extending sections which can be equally distributed about the axis of rotation. As a result, the blood flow through the artificial valve is distributed more evenly over the valve's cross section. As a further great advantage, the relative displacement of the valve members for bringing their blood flow passages into alignment is less. This can be easily appreciated for a valve having two valve members as shown in FIG. 14 and having passages with an overall angular extension of 180° (or somewhat less), however, the passages being subdivided into e.g. four sections of 45° equally spaced apart about the common axis, as shown in FIG. 16. Instead of turning the valve member by 180° to bring the blood flow passages of the two valve members into alignment (as in the case of FIG. 15), it is sufficient to turn the valve members by only 45°.
The theoretical maximum flow capacity of an artificial valve with only two valve members amounts to only about 50% of a fully opened natural valve for the simple reason that each of the two valve members must have a closed area sufficiently large to cover and close the flow passage of the respective other valve member when the valve is in its closed position. Therefore, a preferred valve comprises three of said valve members or, more preferably, even more than three valve members, arranged in series. Providing more than two valve members allows for enlarging the flow capacity of the artificial valve. For instance, in the case of three valve members, only 33% of the cross sectional area of each valve member must be closed, i.e. fluid tight, so that by appropriate arrangement of the valve members relative to each other the entire cross sectional area of the artificial valve may be closed.
However, where the artificial valve includes more than two valve members, e.g. three valve members (two displaceable and one stationary valve member) each having a blood flow passage with an angular extension of 240°, the blood flow passages of each pair of adjacent valve members overlap by 120°. As a result, backflow in a plane substantially perpendicular to the axis of rotation will occur in the valve's closed position even though, when viewed in a direction along the axis of rotation, the valve members completely cover the entire cross section of the valve. To prevent such backflow, the blood flow passages of the valve members may be divided into sections by means of more or less radially extending bridges. This is shown in FIG. 17 representing a top view of an artificial valve 100 with three valve members arranged in series. The blood flow passages 23 of each of the valve members extend over about 240°, however, the blood flow passage 23 is subdivided by a radially extending bridge 24 so as to divide the blood flow passage 23 into two sections of equal size. The bridges 24 are located at positions so as to prevent in the valve's closed position any backflow from the passage 23 of one valve member through the passage 23 of the next adjacent valve member to the passage 23 of the next over adjacent valve member. In the shown situation of three valve members, it is sufficient to have such a bridge 24 at least in the passage 23 of the centrally arranged valve member so as to separate the passage of the upper valve member from the passage of the lower valve member.
Of course, the number of bridges can be larger, and this is even preferred in order to divide the passages into a plurality of angularly extending sections which can be equally distributed about the axis of rotation. As a result, the blood flow through the artificial valve is distributed more evenly over the valve's cross section and, more importantly, the relative displacement of the valve members for bringing their blood flow passages into alignment is less. A principal example of this most complex but most efficient artificial valve with three valve members is shown as a top view in FIG. 18. In this case, the blood flow passage 23 is divided to form two sections of about 120° equally spaced apart by relatively wide bridges, and such sections are further subdivided by bridges 24 so as to form subsections of equal size. Again, the bridges 24 are needed to prevent any backflow which would otherwise occur between adjacent valve members.
One problem arising with the afore-described system is the backflow that occurs through the valve back to the heart chamber at the time when the diastolic pressure in the heart chamber reaches a minimum. This is particularly dangerous for patient's suffering from coronary blood supply problems since the coronary arteries branching off of the aorta right behind the aortic valve require high blood pressure. Those people typically have low blood pressure and little heart pump capacity. It is therefore important that the valve closes quickly. However, the problem of back flow is likewise critical in cases where the valve is provided to replace a valve within the heart, such as the tricuspidalis valve between the right ventricle and the right atrium.